SEXUAL RELATIONS. 29 



cimens not allowing the internal organs to be examined), and 

 there cannot be any reasonable doubt that this species 

 likewise is exclusively female. It should be borne in mind 

 that the male organs, external and internal, are most easily 

 discovered, and that in the above cases I had an abundant 

 supply of excellent specimens. On the other hand, in 

 Ibla Cumi?igii, and in four species of Scalpellum, I was 

 able to demonstrate in the supporting Cirripede the pre- 

 sence of all the male organs, as well as of the female ; and 

 in the vesiculse seminales of several specimens, both in the 

 Ibla and in Scalpellum vulgar e, spermatozoa were contained ; 

 the male organs, however, not being very amply developed. 

 These species, consequently, are not exclusively female, but 

 are hermaphrodite, though having male epizoons attached 

 to them. This statement, I am well aware, is enough, at 

 first, to cast a doubt on all that I have said ; but let any 

 one reflect on the evidence, of which I have here given a 

 summary, and which has been elsewhere given in full, and 

 I think he must admit that at least those epizoons which 

 are exclusively male, and which are attached to Cirripedes 

 exclusively female, are sexually related and form one 

 species ; but if he admit this, he cannot possibly escape 

 from the conclusion that some of the other epizoons, for 

 instance that of Ibla quadrivalvis, are the males of the 

 hermaphrodites to which they are attached, — these epizoons 

 not exclusively impregnating the ova of a female, but aiding 

 the self-impregnation of an hermaphrodite. Hence I have 

 called these males Complemental Males, to show that they 

 do not pair with a female, but with a bisexual individual. 

 Nothing strictly analogous is known in the animal king- 

 dom, but amongst plants, in the Linnean class, Polygamia, 

 closely similar instances abound. 



In the series of facts now given, we have one curious illus- 

 tration more to the many already known, how gradually 

 nature changes from one condition to the other, — in this 

 case from bisexuality to unisexuality. Finally, in the four 

 genera so often named, we meet the following several 

 cases, some of them even the most diverse, occurring in 

 closely allied species. (1st,) a female, with a single male 

 (rarely with two) permanently attached to her, protected 



